The present technology relates to a method and apparatus for non-contact transporting or shaping softened, viscous, or viscoelastic materials using ultrasonic near field levitation. The method and apparatus are particularly suitable for transporting or shaping hot glass.
Fusion draw processes are used to form sheet materials, such as glass, with pristine surfaces of fire-polished quality. Such sheet materials can be used to make 3D shaped glass parts for products such as, for example, mobile phone covers, automotive windows, and architectural applications. Since the shaped glass parts are used to hold and protect a display, or used as windows, the shaped parts must be pristine and have a perfect optical quality.
Several processes are known in the art for reforming glass sheet into 3D parts. Known processes include pressing, sagging, vacuum forming, pressure forming, and combinations of these techniques. The final shape of the reformed glass is a copy of the forming mold. One drawback of prior art forming processes is that it is difficult to obtain parts that have the necessary pristine surface quality. Surface quality is a function of the cleanliness of the forming environment, and also depends on the glass interaction with a mold during the forming process. Especially at high temperature, when the glass is softer, the glass can cool unevenly when in contact with a colder mold, causing higher stresses and changes in the final shape of the glass. Defects in the glass can also be introduced due to oxidation of the mold, sticking of the glass to the mold, and transfer of machining or tool marks from the mold to the glass. In addition, during the forming processes, the glass needs to be moved from step-to-step, and avoiding damage to the edge or surface as the glass is handled can be a challenge.
Another drawback of the reforming processes is that, as a result of the higher temperature glass contacting the colder mold, the molds can become deformed or damaged. Consequently, the molds have a limited life and have to be prepared and exchanged on a regular basis to limit cosmetic defects in the reformed glass. Having to replace the molds on a regular basis increases the cost of the reforming process.
Avoiding contact with the glass during the transporting and reforming operations is desirable because it may likely limit damage to the glass and to the mold, and also likely increase the life of the mold, thereby reducing cost.
Technologies for non-contact or low-contact transport of objects exist in the art. For example, conveying systems using magnetic forces or air cushions are known and used in the art. Air cushions can be generated by air flowing through nozzles along a conveying plate or a rail. Alternatively, sound waves can be used to generate the air cushions for conveying objects. In such systems, the objects to be conveyed are atop a vibrating surface and have a solid, planar surface. Sound waves emanating from the vibrating surface create a gas squeeze film that generates a levitation force that levitates the object above the vibrating surface. One requirement of known levitation systems is that the object to be levitated must have a hard or solid surface. What is needed in the art is a levitation system that can be used to levitate hot or molten glass, or other viscous materials, such as gums, that do not have a hard or solid surface.